The loss of grain from a combine harvester due to unthreshed heads, i.e. grain loss resulting from grain kernels not being threshed from the heads, is related largely to the cylinder to concave clearance and the cylinder speed. Crop variables such as crop variety, crop moisture content and machine loading also affect these losses and complicate making the adjustments for minimizing the losses.
One of the difficulties is the detection and measurement of losses due to unthreshed heads that is taking place. There is presently no entirely satisfactory method of measuring such losses. Conventional grain loss monitors will detect loose kernels of grain but will not detect kernels remaining in the heads. An example of a grain loss monitor utilizing acoustic-electric sensing is disclosed in U.S. Pat. No. 4,004,289.
The procedure most frequently used by combine operators to determine unthreshed head loss is to visually inspect the heads that have passed through the combine for unthreshed and make the adjustments considered to be appropriate.
Another method presently used involves collecting the effluent from the combine in a recepticle. The effluent is first run through a cleaning system to separate the loose grain and is then rethreshed. After the rethreshing, which separates the kernels from the heads, the material is again passed through a cleaning system to isolate the loose grain which represents the grain loss from the unthreshed heads. Although this method provides a quantitative measure, it does not provide a continuous or instantaneous measure, and may not provide a measure that is representative of the entire field due to variations in the crop conditions in different locations of the field. This latter method is also expensive and time consuming.
The detection and counting of seeds utilizing microwave transmitter-sensors is known. Examples of such devices are disclosed in U.S. Pat. Nos. 4,239,010 and 4,246,469. These devices operate by providing an output in response to a disturbance in the microwave standing wave pattern generated by passing seeds.